Draining down heating v Antifreeze?

[Tim Court]

Need some advice - we have a large garage that has a flat above it with its own (1 year old) oil fired combi. It is not being used since we moved in last year and I turned the heating right down to save cash. It is now just on the frost setting but still seems to be firing up at random times. The boiler was serviced last week.
We are eating through oil which has just topped 67.9p+vat per litre! So I am looking at further ways to reduce my consumption and shutting the system off completely seems to be an option especially since the building is empty...
Worried about freezing and am concerned if I drain down the heating I will end up with rust in the radiators. I have seen this on a construction site refurb that required some harsh chemical flushing when we came to recommission.
Is there an additive which has an anti freeze component that I can pump round and leave the heating side full?

 

[SJB060685]

What’s the frost stat set to? The boiler is probably coming on to heat the slave tank.

 

[Tim Court]

What’s the frost stat set to? The boiler is probably coming on to heat the slave tank.

I think it is 12 degC but not sure... I think that is the factory setting.

 

[John.g]

What make/model of boiler.

 

[Tim Court]

The boiler is a Worcester Greenstar Heatslave II 12/18

 

[SJB060685]

The frost stat is usually set to 5°c. As I said the boiler could still be coming on to heat the slave tank.

 

[John.g]

From the EXTERNALLY installed one.....

" Frost protection ▶ The boiler has built in frost protection to protect the boiler, the boiler must have power for this to operate. ▶ If you are leaving the property unoccupied during cold weather, please leave your programmer on constant and your room thermostat set to 15°C. ▶ If the temperature within the boiler falls below 8°C the pump will run to circulate water and prevent the system freezing. ▶ If the temperature within the boiler falls below 4.5°C the boiler will fire immediately, bringing the boiler temperature up to 12°C to avoid the possibility of the system freezing. ▶ This process will be repeated until such time that the boiler temperature does not drop below 4.5°C."

 

[Tim Court]

From the EXTERNALLY installed one.....

" Frost protection ▶ The boiler has built in frost protection to protect the boiler, the boiler must have power for this to operate. ▶ If you are leaving the property unoccupied during cold tweather, please leave your programmer on constant and your room thermostat set to 15°C. ▶ If the temperature within the boiler falls below 8°C the pump will run to circulate water and prevent the system freezing. ▶ If the temperature within the boiler falls below 4.5°C the boiler will fire immediately, bringing the boiler temperature up to 12°C to avoid the possibility of the system freezing. ▶ This process will be repeated until such time that the boiler temperature does not drop below 4.5°C."

Thanks for the info . The boiler is an internal instal but I expect the parameters will be broadly similar. This is what I am trying to stop as I have gone through £700 worth of oil since Christmas but I’m a bit wary of draining down... funny how cars sit quite happily with antifreeze in their cooling system and I wondered if some central heating additives have an antifreeze component.

 

[John.g]

I doubt very much if the frost stat is devouring much oil, if vat is the same as here at 13.5% then £700 of oil at 77C/litre would equal ~ 910 Litres. My 1000 litre oil tank just happens to calibrate at exactly 1 MM/litre so very easy to get quite accurate measurements by just taking a ullage measurement. I used 523 litres from 21/12/21 to 21/2/22, or 8.44 Litres/day, say 86kwh/day or house input of ~65 kwh/16 hour heating day with a 16 year old SE 20kw firebird boiler, house is a 50 year old, 4 bed semi detached. Your consumption does seem pretty high except you are running the heating 24/7.

 

[Tim Court]

Thanks for your input. In fact the heating is off in the flat but from what I can see it appears to fire into life when the temp is around 8 deg. Our vat is 5% so I have used 1000 litres since Christmas and I have no way of finding out how much is being wasted on an empty flat and how much we are using in our house.
I had another trawl online and it appears that quite a few holiday home owners who close up over winter use a variety of antifreeze additives specifically for central heating systems so a trip to Screwfix is on the cards...

 

[John.g]

What was being heated since Christmas to use 1000 litres?, the empty flat? and/or just frost protection?. 1000 litres over say 65 days is a huge amount of oil, ~ 134kwh/day, net.
The frost protection if, as I think it is, monitoring the water temperature, it still wouldn't consume a lot of oil as its only heating the water to 12C which means the rads would emit little or no heat even if the zone valves are opening. If the frost stat is monitoring the air temperature and the thermostat isn't very close to the boiler casing the it will consume more.